Already done. Let's continue.
There's no such thing as a "rest photon". That's, hmm, the second postulate of special relativity? Heard of that?
Relativistic mass is a useless and outdated concept that is not used by any physicist I know of. But even if you wanted to use it, you're going to have a hard time defining it for photons - it's zero times infinity - unless you simply declare it's equal to the energy (in which case why bother with it at all?).
This is literally something young primary school children struggle with.
The slope of
what line?? And even if there were one orange in this crate you find so confusing, I could ask you to look at the ratio N
apples/(N
oranges-1)

!
Numbers are an abstraction. One apple is not the number "1" - it's a rather complex object, constantly exchanging molecules with its environment, much larger than some other apples, smaller than others, perhaps with a tiny bite out of it, perhaps with a worm in it, which we have chosen to label as "one apple". We can then use the rules of math to manipulate numbers, and those manipulations correspond to some extent to certain manipulations of the objects we've labeled - but never exactly (numbers don't get eaten, or rot, or grow into trees full of other numbers).